Accumulator or battery with sulfuric acid electrolyte containing phosphoric acid

ABSTRACT

A lead battery or accumulator in which each electrode is wrapped in a web of say, fiber glass, the electrolyte consists of a mixture of sulphuric acid and phosphoric acid, and the electrolyte is made thixotropic by addition of a jell-forming material, such as silicon dioxide with a particle size of 0.01 to 0.02 microns. The web provides pockets which hold the electrolyte, and between adjacent electrodes there are disposed perforated, undulant spacers. The electrode grids are preferably made of a lead-calcium base. Preferably the electrodes are charged while dry, then wrapped in the fiber web, then assembled into the battery housing; then the electrolyte is introduced into the housing; and the housing is ventilated.

United States Patent [191 Jache 1 ACCUMULATOR OR BATTERY WITH SULFURICACID ELECTROLYTE CONTAINING PHOSPI-IORIC ACID [76] Inventor: Otto Jache,1m Thiergarten,

Budingen/Oberhessen, Germany [22] Filed: Nov. 30, 1970 [21] Appl. No.:93,888

Related US. Application Data [63] Continuation-impart of Ser. No.747,974, July 26,

1968, abandoned.

[30] Foreign Application Priority Data Dec. 1, 1967 Germany A 57 56 121[52] US. Cl. 136/26, 136/157 [51] Int. Cl. H011 39/04 [58] Field ofSearch ..136/26, 6, 154, 157, 136/17 [5 6] References Cited UNITEDSTATES PATENTS 3,172,782 3/1965 Jache 136/6 3,177,096 4/1965 Jache....136/6 3,257,237 6/1966 Jache 136/6 3,011,007 11/1961 Evers et a1. 136/263,402,077 9/1968 Kida et a1. 1 136/6 3,201,281 8/1965 Solomon et a1136/6 1 Oct. 16, 1973 3,265,535 8/1966 Sundberg 136/148 3,180,760 4/1965Rauter 136/6 3,530,002 9/1970 Little 136/157 3,556,860 l/1971 Amlie136/157 OTHER PUBLICATIONS Tudor et al., Electrochemical Technology JulyAug., 1966, p.p. 406-411.

Primary ExaminerA. B. Curtis Assistant ExaminerC. F. LefevourAttorney-Shlesinger, Fitzsimmons & Shlesinger 5 7] ABSTRACT A leadbattery or accumulator in which each electrode is wrapped in a web ofsay, fiber glass, the electrolyte consists of a mixture of sulphuricacid and phosphoric 3 Claims, 4 Drawing Figures PATENTEDBBI 15 19153.765342 SHEET 10F 2 INVENTOR OTTO JACHE BY fi' I'TORNEY CAPACITY IN "/0PATENTEDHBI 16 ms 3.765.942 SHEET 2 BF 2 50- B2 BI NO. OF CYCLES FIG. 4

INVENTOR OTTO JACHE BY TTORNEY ACCUMULATOR R BATTERY WITH SULFURIC ACIDELECTROLYTE CONTAINING PI-IOSPHORIC ACID This application is acontinuation of my copending application Ser. No. 747,974, filed July26, 1968 now abandoned, for Accumulator or Battery.

The invention relates to a lead battery or accumulator with improvedlife and improved uniformity in capacity during its cycles of charge anddischarge.

Preferably in lead accumulators, whose positive plates consist of ametallic grid and of an essentially active mass of lead suboxide, leadalloy plates are used for the electrode grids, which contain, as theessentially stabilizing part of the alloy, antimony, the antimonycontent being at most between S and 12 percent. Positive plates, with anelectrode grid made from such a lead antimony alloy, can contain ifoccasion arises, as a further stable part of the alloy arsenic, copper,silver, tin, etc. Such batteries have a recognized good life expectancyas regards cycles, that is, as regards continuous successive dischargingand charging.

Efforts have been made for quite a long time, however, to eliminateantimony completely in the production of lead accumulators, sinceantimony is quite expensive in proportion to lead and since with the useof electrode grids containing antimony the self-discharge of theaccumulator is considerable. The introduction, though, of leadaccumulators whose electrode grids are antimony-free has hithertosuffered from the fact that their positive plates have a very bad life.The active mass of the positive plates loses very quickly its cohesionin the course of the cycling. It loses in increasing amount its capacityto store electrical energy, and to give up again its stored energy, thatis, the capacity of the lead accumulator becomes constantly smaller.

It is already known that this loss can be offset by arranging thepositive plates in pockets consisting of a fleece of glass fiber or of aweb of synthetic material. Thereby, however, only erosion of the positvemass is hindered; the deterioration phenomenon is still not preventedpractically.

It is also already known that phosphoric acid may be added to theelectrolyte of lead accumulators. Through phosphoric acid additionoriginally it was desired to prevent the harmful sulphating ofaccumulators having the lead-antimony alloy electrode grids. Through theaddition of the phosphoric acid, moreover, better fixation of thepositive mass and thereby a lessening of its spalling off duringcycling, as well as a diminution of corrosive action on the grid rackand current conductor can be obtained, whereby all together animprovement in the lifeof the accumulator can be achieved.

The phosphoric acid has heretofore been supplied in different ways tothe electrolyte. For example, it has been added, in a dry state in theform of one of its salts, to the lead oxide used for filling of thecapillary plates, or, in fluid form, to the lead paste mixture used forstuffing the positive grid plates.

Another process was to immerse the positive electrodes produced in theusual fashion, before their formation, for a longer time in a strongphosphorcontaining sulphuric acid.

It is also possible to add the phosphoric acid directly to theelectrolyte used for activating the accumulator.

The hitherto known lead accumulators with a phosphoric-acid-containingelectrolyte exhibit, however, an unsatisfactory capacity and anunsatisfactory life in their cycling. In the cycling after an originallybrief capacity increase, a heavier capacity decline during the first tendischarges is perceptible. The decrease in capacity is in directrelation to the amount of the phosphoric acid added. With smallphosphoric acid additions, the capacity decrease is not so pronounced;while with greater phosphoric acid additions the capac- 1ty can decreaseup to 50 percent of the initial capacity.

Accumulators are already known which contain an electrolyte withthixotropic characteristics, that is, an electrolyte converted to thethixotropic state by addition of an extremely finely divided insolubleoxide, for example, of silicic acid, or aluminum oxide. The electrodesare wrapped with a fleece or web of glass fibers or another suitableacid resistant fiber. The fleece or web on the electrode holds theelectrolyte fast in the vicinity of the plates, and spreads theelectrolyte equally over the whole surface of the plates because of itswick-like action, and thereby promotes current passage and diffusion,since the pores of the active mass are filled with freely movablejell-free electrolyte.

The subject matter of the invention is a lead accumulator which ischaracterized by the combination'of the following in themselves knowncharacteristics:

1. The grid of the electrode consists of fine lead, dispersion hardenedlead or of an antimony-free lead alloy.

2. Each electrode is wrapped in a fleece or web. The term web ashereinafter used is intended to include a fleece.

3. The electrolyte consists of sulphuric acid to which 20 to 35g/l. ofphosphoric acid are added and 4. The electrolyte is made thixotropic byaddition of a jelling material.

In an accumulator built in accordance with the present invention thecapacity does not decrease suddenly during cycling but increases stillfurther and finally does not vary any more.

The invention will now be explained further with reference to thedrawings in which:

FIG. 1 is a section extending parallel to the plane of the plates of anaccumulator made according to the invention, individual parts beingbroken away for better illustration;

FIG. 2 is a section on the line IIII in FIG. 1;

FIG. 3 is a section on the line III-III in FIG. 2; and

FIG. 4 is a diagrammatic illustration of the capacity of differentaccumulators in dependence on the number of the cycles.

The accumulator illustrated in the drawings consists of a housing 1 andof a cell cover 2 which are cemented or welded together. The negativeelectrodes 3 and the positive electrodes 3' are fastened together insets in the usual manner by means of bridges 4 and 4'. The negativeterminal post 5 and the positive terminal post 5' extend through thecover 2 and carry on their upper ends contacts 6. For liquid andgas-tight sealing, the posts are mounted in seals 7 in the cover. Theindividual electrodes 3 and 3' are covered by a web or fiber fleece 8,8, resulting in pockets for taking up the electrolyte 9, whichpreferably are open above.

Preferably, as shown in FIG. 2, the fiber fleeces 8 and 8' are extendedabout the electrodes 3 and 3' and the space between two neighboringelectrodes 3, 3' is covered laterally and on its underside by anadditional web 10 for the development of pockets opening only at thetop. Between two adjacent electrodes 3 and 3' there is disposed anundulant and perforated spacer 11.

The pockets built up from the fleece or web are covered by a plate 12which has holes 13, 13' bored through it. In the center of the coverthere is a valve block 14 which is secured by a fluted lip 15 againsttwisting or withdrawal. The valve block comprises a body insert 16, thevalve proper formed by an inverted cup-shaped member 17, the cover plate18 and the protective cage 19.

The valve body has shoulders 20 which in the seating of the valve properslide under the opposed shoulders 21 provided on the cell cover in theform of a bayonet joint, so that between the sealing surfaces 22 and 23there is compressed a sealing ring 24. Thus, a sealed closure isprovided between the valve insert 14 and the cell cover 2. A boss 25provided in the cover plate 18 presses the valve body 17 down, wherebythe rim 26 of member 17 is sealingly engaged in a ring groove 28 ofblock 14, such groove being filled with a silicon oil 27.

About the positive pole post 5 with the contact 6 there is built up aprotecting ring 29 provided with a slot 30 which with the correspondingopposed contact insures the mounting of the accumulator in its correctposition and prevents the poles from being exchanged inadvertently. Thecover plate 18 is fixed in the valve block 14 by means of peripherallugs 31 and of a ringshaped collar 32 in such a manner that when thevalve opens, the excess pressure will be relieved by the escape of gasesbetween the outer periphery of plate 18 and the insert body 14.

The electrolyte consists of sulphuric acid with a density of 1.24 to1.30, preferably approximately 1.28 at 20C. To this there are added, perliter, 20 to 35 grams of phosphoric acid; and by addition of a finelydivided oxide insoluble in the electrolyte, preferably silicic acid, theelectrolyte is converted to a thixotropic state. The most favorablecontent of phosphoric acid in the electrolyte amounts approximately to25 g/l.. A phosphoric acid content below 20 g/l. is unsatisfactory,while a phosphoric acid content of over 35 g/l. results in aconsiderably decrease of the capacity.

For converting the electrolyte to a jell state, preferably finelydivided pyrolytically produced silicic acid is used having a particlesize of 0.01 to 0.02 micron and a surface of 200m /g. For jell-buildingmaterial if occasion arises, other suitable metallic oxides, forexample, aluminum oxide, or organic jell builders, which aresufficiently stable in the electrolyte, can be used.

The amount of the added silicic acid depends on the particle size andthe surface area and will be approximately from 3 to 10 percent,preferably 6 percent. With use of a silicic acid addition below 3percent too long stabilizing times are required for the building up of aconsistent jell, while with an addition of over 10 percent a prematurealteration of the jell can take place.

For covering the electrodes a fiber glass is preferably used, in whichthe thickness of an individual fiber is approximately l5 microns and theoffset between the individual fibers amounts to 150 microns. Thinnerglass fibers can also be used up to 10 microns or thicker up to 20microns. Precautions should be taken, however, to insure that the poresizes of the fleece, determining the center-to-center offset betweenindividual fibers, is somewhere between 100 and 200 microns.

The grids of the electrodes are made of fine lead, dispersion-hardenedlead, or of an antimonyfree lead base, preferably of a lead-calcium baseproduced from 0.08% calcium, the rest lead. Hereinafter, when the termlead grids" is used, it is meant to cover any and all of these possibletypes of grids.

It has appeared especially advantageous that the active masses of theelectrodes already contain stored at the time of filling of theelectrolyte their full electrochemical energy, that is, if in theproduction of the accumulator dry-charged electrodes are used.

in the following the preparation of the electrolyte will be explained byan example. There are placed in a mixing vessel 90 liters of sulphuricacid; and there are added little by little with continuous stirring 5 kgof very finely divided silicic acid with a surface area of 200 m /g.Finally 1.6 liters of 85% orthophosphoric acid with a concentration of1.7 is stirred in. The thusproduced electrolyte is flowed into the cellsof the lead accumulator while being continuously stirred until they arefilled. it possesses a viscosity of about 1.500 CP.

It has proved especially advantageous, before filling of theelectrolyte, first to evacuate the accumulator housing having the setsof electrode plates already in place therein; whereupon the electrolyteis poured in. Caution is to be taken that the electrode plates of theaccumulator are brought into contact with the electrolyte as far aspossible uniformly and in as brief as possible time. After filling thehousing with the electrolyte the housing is exposed to air, so that thepores of the active masses are filled with electrolyte fluid. In thisway only the fluid portions of the electrolyte press into the pores,while the silicic acid portions remain in the pockets built out of theglass fiber, and within the pockets, on the basis of the existing fluid,the jell building already sets in. Especially is it advantageous thatwithin the fleece or web lying on the electrodes a higher jellconcentration is built up. This results in an improved fixation of thejell in its area.

' in order to reduce the loss of water as much as possible to a minimumduring the charging of an accumulator built according to the invention,the charging is stopped upon attainment of a cell voltage of at most 2.5volts.

The accumulator according to the invention is safe in any position, andcan be charged and discharged in any suitable position.

For proof of the advance achieved by the invention several accumulatorswith the construction shown in FIGS. 1 to 3 were produced by use ofuniform plate materials. An accumulator, which is designated asaccumulator A, was filled with an electrolyte which consisted ofsulphuric acid converted to the thixotropic state by addition of silicicacid. A further accumulator, which is designated as accumulator C, wasfilled with an electrolyte which consisted of sulphuric acid convertedto the thixotropic state by addition of silicic acid, and to it therewas further added, according to the invention, phosphoric acid. Afurther accumulator was filled with sulphuric acid, to which had beenadded 6.5 g/l. of phosphoric acid. This accumulator whose electrolytecontained no silicic acid has been designated as accumulator Bl. Anotheraccumulator was filled with sulphuric acid which had added to it 26 g/l.of phosphoric acid. This accumulator, whose electrolyte also containedno silicic acid has been designated as accumulator B2.

In FIG. 4 the capacity graphs of the accumulators A,

C, B1 and B2 are illustrated in connection with the number of thecharging and discharging cycles. From this Fig. it is apparent that thecapacity of the accumulator A remains constant up to about 35 cycles,and then decreases very severely. After 85 cycles the accumulator A haspractically attained the end of its life. In contrast to this theaccumulator C of the invention has at the beginning a lower capacity ofabout percent. It attains after about 5 cycles the initial capacity ofthe accumulator A, and in contrast to this, increases then constantly toapproximately 115 percent and remains constant finally to over 150cycles. With accumulators B1 and B2, the capacity first decreases veryheavily and then increases to about the 10th cycle. As is apparent fromthe curve for the accumulator B2 the addition of a higher amount ofphosphoric acid causes first a larger capacity decline, then thecapacity again increases to a higher value than with use of anelectrolyte with a smaller phosphoric acid addition.

In the following table the capacity of the accumulators in ampere hoursis given after the first, fifth, tenth, and fifteenth discharges. Theaccumulators contained a fixed sulphuric acid electrolyte throughaddition of silicic acid with the phosphoric acid concentrations givenin column 1. From the table it is apparent that the range used accordingto the invention of approximately to 35 g. of phosphoric acid per literis the most favorablc.

While the invention has been described in connection with certainspecific embodiments thereof, it will be understood that it is capableof further modification, and this application is intended to cover anyvariations, uses, or adaptations of the invention following, in general,the principles of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertains and as may be applied to the essentialfeatures hereinbefore set forth, and as fall within the scope of theinvention or the limits of the appended claims.

Having thus described my invention, what I claim is:

l. A lead battery comprising a housing containing spaced electrodeshaving lead grids free of antimony,

an electrolyte comprising a mixture of sulphuric acid and phosphoricacid rendered thixotropic by admixture of jelling material,

the quantity of phosphoric acid in the electrolyte, be-

fore charging, being 20 to 35g per liter of said electrolyte so thatafter a lower initial capacity, the capacity of said accumulatorincreases and then remains substantially constant to over about cycles.

2. A lead battery according to claim 1, wherein the jelling material issilicic acid.

3. A lead battery comprising a housing containing spaced lead electrodesfree of antimony, a sulphuric acid electrolyte rendered thixotropic byadmixture of a jelling material, and containing a quantity of phosphoricacid, the amount of phosphoric acid in the electrolyte before charging,being 20 to 35g. per liter of said electrolyte so that after a lowerinitial capacity, the capacity of said accumulator increases and thenremains substantially constant to over about I50 cycles. =1

2. A lead battery according to claim 1, wherein the jelling material issilicic acid.
 3. A lead battery comprising a housing containing spacedlead electrodes free of antimony, a sulphuric acid electrolyte renderedthixotropic by admixture of a jelling material, and containing aquantity of phosphoric acid, the amount of phosphoric acid in theelectrolyte before charging, being 20 to 35g. per liter of saidelectrolyte so that after a lower initial capacity, the capacity of saidaccumulator increases and then remains substantially constant to overabout 150 cycles.